In the fall of 1989, an aerial surveillance program was implemented to locate oil sheens (or slicks) originating from shorelines affected by the Exxon Valdez spill. The objectives of the program were to identify any oil on the water that warranted response and to identify those sections of shoreline that would be priority candidates for further cleanup in 1990. The program initially surveyed the entire affected area, but, because proportionally fewer sheens were spotted in the Gulf of Alaska, the program was refocused on Prince William Sound in early 1990.

The surveillance program consisted of frequent low-altitude flights with trained observers in a deHavilland Twin Otter outfitted with observation ports and communication equipment. The primary surveillance technique used was direct visual observation. Other techniques, including photography, were tested but proved less effective. The flights targeted all shorelines of concern, particularly those near fishing, subsistence, and recreational areas. The observers attempted to locate all sheens, estimate their size and color, and identify the source of the oil found in the sheen. Size and color were used to estimate the volume of oil in each sheen. Samples were collected whenever possible during the summer of 1990 using a floating Teflon™ sampling device that was developed for easy deployment from a boat or the pontoon of a float plane. Forty four samples were analyzed by UV-fluorescence spectroscopy. Eleven of these samples were also analyzed by GC/MS. In general, the analyses confirmed the observers' judgement of source.

The flights from late September 1989 through early September 1990 identified 827 petroleum hydrocarbon sheens. About two-thirds of the sheens were related to the Exxon Valdez or were of indeterminate source. For the purposes of analyses these were combined and treated as if their origins were all from the Exxon Valdez. The numbers and volumes of these sheens decreased dramatically with time after the onset of winter storms.

The Exxon Valdez related sheens sighted during the spring and summer of 1990 contained volumes averaging less than two litres of oil each. By the summer of 1990, the number and size of Exxon Valdez sheens were smaller than those associated with normal vessel activity in Prince William Sound. There was no disruption of commercial fishing activities because of Exxon Valdez related sheens in 1990. The program was discontinued in September 1990 because the number and volume of spill-related sheens had declined to low levels.